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Homeostasis - kidneys and water balance

Bowman's capsule

The cup-shaped first part of the kidney tubule found in the outer cortex region

Blood vessels

The tubes through which blood is carried around the body eg arteries, veins and capillaries

Renal tubule

The main part of the kidney tubule where reabsorption takes place, found in the medulla of the kidney

Capillary

Very small blood vessel with walls made of a single layer of epithelial cells. Exchange of materials, such as nutrients, oxygen and carbon dioxide, takes place between the blood and the cells of the body across the capillary walls.

Glomerulus

The knot of capillaries in the Bowman's capsule.

Medulla

The inner region of the kidney containing the renal tubules

Nephron

The kidney tubule in which reabsorption of substances and the balancing of the concentration of the blood takes place

Hormone

A chemical messenger produced by a particular gland or cells of the endocrine system. Hormones are transported throughout the body in the blood stream but they produce a response only in specific target cells

Cortex

The outer region of the kidney containing the Bowman's capsules

Antidiuretic hormone

Hormone produced in the hypothalamus that is produced by the pituitary gland when the body needs to lose less water. It affects the permeability of the distal convoluted tubule and the collecting duct of the kidney to water

How the kidney works

Each kidney contains about a million tiny structures called nephrons. A nephron has a cup-shaped Bowman's capsule leading into the renal tubule. The two sections of each nephron extend across the two different regions of the kidney:

the Bowman's capsules are found within the outer cortex region

the renal tubules run from the cortex into the darker medulla

How does the kidney balance the blood?

Placed end to end, the nephrons of one kidney would stretch about 8 km. Their function is to remove waste products such as urea and balance the water and mineral ion concentration of the blood. How does the process work?

A branch of the renal artery supplies the nephrons with blood. In the Bowman's capsule, the artery splits up into a network of capillaries called the glomerulus. These capillaries join into a single vessel again as they leave the capsule, and then split into a second set of capillaries that are wrapped around the renal tubule. The blood leaves the tubule in the renal vein.

The size of blood vessels supplying the glomeruli is larger than that of the capillaries in the glomeruli themselves. This creates high blood pressure, in the glomerular capillary network which forces water and solutes into the Bowman's capsule.

c) Look at the picture below. Click on the picture where you would expect to find the greatest concentration of glucose in the renal tubule.

Correct, the greatest concentration of glucose in the renal tube can be found in the Bowman's capsule or just below.

That's not right, try again.

d) As the glomerular filtrate passes along the tubule, most of the water is absorbed back into the blood. How does this affect the concentration of urea?